How do you convert megajoules to gigajoules?

To convert megajoules (MJ) to gigajoules (GJ), multiply the energy in megajoules by 0.001 (gigajoules = megajoules × 0.001).

What is 5 megajoules in gigajoules?

5 megajoules (5 MJ) is equal to 0.005 gigajoules (0.005 GJ).

Which is larger, 1 megajoule (MJ) or 1 gigajoule (GJ)?

One gigajoule (GJ) is larger than one megajoule (MJ). Specifically, 1 GJ equals 1,000 MJ, while 1 MJ is 0.001 GJ.

How do I convert back from gigajoules (GJ) to megajoules (MJ)?

To reverse the calculation from GJ to MJ, multiply your gigajoule value by the inverse factor 1,000 (or divide by 0.001). You can also click the Swap button in the tool above to flip directions in one click.

How many decimal places should I round MJ to GJ results to?

For everyday comparisons and quick estimates, rounding to 2 decimal places is usually sufficient (for example, 5 MJ ≈ 0.01 GJ). For engineering, laboratory, or machining specifications, select 4 or 6 decimals—or Scientific (10ⁿ) mode—in the calculator toolbar above.

Megajoules to Gigajoules Converter

Enter the energy in megajoules below to convert it to gigajoules.

Gigajoules to Megajoules (GJ → MJ)

Convert Megajoules to Gigajoules

Enter a value in megajoules (MJ) to convert to gigajoules (GJ).

Value (MJ)

From

Result

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0.005gigajoules

5 MJ = 0.005 GJ

Result updates automatically

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Suggested Conversions

Reference:NIST CODATA (CODATA Energy & Thermodynamic Constants)

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Megajoule to Gigajoule Conversion Table

Table showing various megajoule measurements converted to gigajoules. Click any preset value or arrow to load it into the converter.

Megajoules (MJ)	Gigajoules (GJ)
1 MJ	0.001 GJ
2 MJ	0.002 GJ
2.5 MJ	0.0025 GJ
5 MJ	0.005 GJ
10 MJ	0.01 GJ
15 MJ	0.015 GJ
20 MJ	0.02 GJ
25 MJ	0.025 GJ
30 MJ	0.03 GJ
50 MJ	0.05 GJ

How to Convert Megajoules to Gigajoules

To convert megajoules to gigajoules, multiply the energy by the following conversion ratio: 0.001 gigajoules/megajoule.

Since one megajoule is equal to 0.001 gigajoules, you can use this simple formula to convert:

gigajoules = megajoules × 0.001

The energy in gigajoules is equal to the energy in megajoules multiplied by 0.001.

For example, here's how to convert 5 megajoules to gigajoules using the formula above.

gigajoules = (5 MJ × 0.001) = 0.005 GJ

How Many Gigajoules Are in a Megajoule?

There are 0.001 gigajoules in a megajoule, which is why we use this value in the formula above.

1 MJ = 0.001 GJ|1 GJ = 1,000 MJ

Our megajoule to gigajoule calculator automatically converts your energy measurements with full decimal and scientific precision across US customary, imperial, and SI metric standards.

Megajoules and gigajoules are both units used to measure energy. Keep reading to learn more about each unit.

What Is a Megajoule?

A megajoule is a unit of energy equal to 1,000,000 joules (J), the base unit for energy. Equal to 1,000,000 Joules. [1]

The megajoule is classified as an International System of Units (SI) unit of energy. Megajoules can be abbreviated as MJ; for example, 1 megajoule can be written as 1 MJ.

In the metric system, "mega" is the standard SI prefix for millions, or 10⁶. This makes the megajoule (MJ) a convenient decimal multiple of the joule (J).

In practice, megajoules (MJ) are widely used across large-scale industrial, bulk, and macro-level energy specifications within International System of Units (SI) workflows, engineering documentation, and technical data sheets.

Learn more about megajoules in our Energy Converter.

What Is a Gigajoule?

A gigajoule is a unit of energy equal to 1,000,000,000 joules (J), the base unit for energy. Equal to 1,000,000,000 Joules, common in natural gas billing. [2]

The gigajoule is classified as an International System of Units (SI) unit of energy. Gigajoules can be abbreviated as GJ; for example, 1 gigajoule can be written as 1 GJ.

In the metric system, "giga" is the standard SI prefix for billions, or 10⁹. This makes the gigajoule (GJ) a convenient decimal multiple of the joule (J).

In practice, gigajoules (GJ) are widely used across large-scale industrial, bulk, and macro-level energy specifications within International System of Units (SI) workflows, engineering documentation, and technical data sheets.

Learn more about gigajoules in our Energy Converter.

When converting energy between megajoules (MJ) and gigajoules (GJ), keep full floating-point precision (1 MJ = 0.001 GJ; 1 GJ = 1,000 MJ) during intermediate calculations and round only the final gigajoule figure to match your instrument tolerance.

More Megajoule & Gigajoule Conversions

Need to calculate in the opposite direction? Use our gigajoules to megajoules calculator to switch your starting unit immediately. You can also explore related tools such as converting gigajoules to megajoules, converting joules to calories, or converting calories to joules.

Convert from Megajoules

Convert to Gigajoules

Frequently Asked Questions

There are 0.001 gigajoules (GJ) in 1 megajoule (MJ). Conversely, 1 gigajoule (GJ) is equal to 1,000 megajoules (MJ).

Energy Converter

Quick Info

Direct Factor: 1 megajoule (MJ) equals 0.001 gigajoules (GJ).
Inverse Factor: 1 gigajoule (GJ) equals 1,000 megajoules (MJ).
Formula: gigajoules = megajoules ÷ 1000.
Verified Precision: Anchored to official NIST SP 811 and ISO/IEC 80000 standards.

Units Comparison

Megajoule (MJ)

Equal to 1,000,000 Joules.

Gigajoule (GJ)

Equal to 1,000,000,000 Joules, common in natural gas billing.

Joule (J)

Coherent SI unit of energy and work (1 W·s = 1 N·m).

References

[1]NIST CODATA · CODATA Energy & Thermodynamic Constants
Source
[2]NIST SP 811 · NIST SP 811 App. B.9 (Energy, Work & Heat)
Source
[3]BIPM · Derived SI Unit: Joule (J)
Source

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References

NIST · BIPM · ISO

[1]
NIST CODATA (CODATA Energy & Thermodynamic Constants)·Energy Metrology Standard — Megajoules (MJ) to Gigajoules (GJ)
NIST CODATA Standard
[2]
NIST SP 811 (NIST SP 811 App. B.9 (Energy, Work & Heat))·Unit Specifications: Megajoule (MJ) & Gigajoule (GJ)
NIST SP 811 Specification
[3]
BIPM (Derived SI Unit: Joule (J))·Conversion Factors & Mathematical Basis (MJ to GJ)
BIPM Reference

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